When nighttime marine accidents are studied, it is found that such accidents frequently occur because the navigator's vision is dazzled by increased numbers of recently developed coast lights. This reduces a navigator's ability to recognize navigational lights of the conventional type. There has been a need to establish an identification method which can be visually recognized clearly by navigators at sea.
For such identification, it is most effective to synchronize the flashes from a plurality of navigational lights. Simultaneous and/or rhythmically moving flashes of the navigational lights are effective in helping navigators recognize a light line or a light plane.
However, in order to provide such synchronization, independent lights such as light buoys must be linked with each other by wire or radio communication means.
Except for a few cases, wire communication is undesirable by reason of expense and difficulty in construction. On the other hand, radio communication requires the installation of an exclusive communication system, but the existing Wireless Telegraphy Act renders such installation very difficult.
It has been proposed to synchronize navigational lights by the use of radio waves sent from non-directional radio beacons or external radio waves sent from broadcasting stations such as time casting radio waves.
However, these radio waves have different frequencies which depend on their location, and are susceptible to jamming. Each receiver must thus have a radio wave detector device with high accuracy and highly accurate adjustability. Accordingly, prior to the manufacture and installation of each receiver, it is necessary to measure radio waves in the area where navigational lights and their receivers are installed, and to manufacture a synchronizer suitable to the measured radio waves.
Moreover, when installing navigational lights, the synchronizer should be fine-tuned at the installation site, and such adjustment requires a great deal of labor and time, particularly if the installation site is abroad or remote from the factory.